Merge pull request #47 from gdgib/G2-1624-BasicPlugins

G2-1624 Implement basic plugins

ha-plugin/src/main/java/com/g2forge/habitat/plugin/IPluginLoader.java

@@ -0,0 +1,7 @@
+package com.g2forge.habitat.plugin;
+
+import com.g2forge.alexandria.adt.collection.ICollection;
+
+public interface IPluginLoader<P> {
+	public ICollection<? extends P> load();
+}

ha-plugin/src/main/java/com/g2forge/habitat/plugin/IPluginService.java

@@ -0,0 +1,7 @@
+package com.g2forge.habitat.plugin;
+
+import com.g2forge.alexandria.adt.collection.ICollection;
+
+public interface IPluginService {
+	public ICollection<PluginDescriptor<?, ?>> load();
+}

ha-plugin/src/main/java/com/g2forge/habitat/plugin/IPluginSystem.java

@@ -0,0 +1,5 @@
+package com.g2forge.habitat.plugin;
+
+public interface IPluginSystem {
+	public <P> IPluginLoader<P> load(Class<P> type);
+}

ha-plugin/src/main/java/com/g2forge/habitat/plugin/PluginDescriptor.java

@@ -0,0 +1,33 @@
+package com.g2forge.habitat.plugin;
+
+import java.util.List;
+
+import com.g2forge.alexandria.java.function.IConsumer2;
+import com.g2forge.alexandria.java.function.IFunction1;
+import com.g2forge.alexandria.java.function.ISupplier;
+
+import lombok.Builder;
+import lombok.Data;
+import lombok.RequiredArgsConstructor;
+import lombok.Singular;
+
+@Data
+@Builder(toBuilder = true)
+@RequiredArgsConstructor
+public class PluginDescriptor<P, B> {
+	@Data
+	@Builder(toBuilder = true)
+	@RequiredArgsConstructor
+	public static class Dependency<T, U> {
+		protected final Class<U> type;
+
+		protected final IConsumer2<? super T, ? super U> callback;
+	}
+
+	@Singular
+	protected final List<Dependency<B, ?>> dependencies;
+
+	protected final ISupplier<B> constructor;
+
+	protected final IFunction1<? super B, ? extends P> builder;
+}

ha-plugin/src/main/java/com/g2forge/habitat/plugin/PluginSystem.java

@@ -0,0 +1,44 @@
+package com.g2forge.habitat.plugin;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import com.g2forge.alexandria.adt.collection.DStreamCollection;
+import com.g2forge.alexandria.adt.collection.ICollection;
+import com.g2forge.alexandria.annotations.note.Note;
+import com.g2forge.alexandria.annotations.note.NoteType;
+import com.g2forge.alexandria.java.function.ISupplier;
+import com.g2forge.alexandria.java.type.ref.ITypeRef;
+import com.g2forge.alexandria.service.BasicServiceLoader;
+import com.g2forge.alexandria.service.IServiceLoader;
+
+import lombok.Getter;
+
+public class PluginSystem implements IPluginSystem {
+	@Getter(lazy = true)
+	private static final IPluginSystem standard = new PluginSystem();
+
+	@Note(type = NoteType.TODO, issue = "G2-1628")
+	protected <P, B> P instantiate(PluginDescriptor<P, B> descriptor) {
+		final ISupplier<B> constructor = descriptor.getConstructor();
+		final B builder = constructor.get();
+		return descriptor.getBuilder().apply(builder);
+	}
+
+	@Override
+	public <P> IPluginLoader<P> load(Class<P> type) {
+		return new IPluginLoader<P>() {
+			@Override
+			public ICollection<? extends P> load() {
+				final IServiceLoader<IPluginService> loader = new BasicServiceLoader<>(IPluginService.class);
+				final List<Object> plugins = new ArrayList<>();
+				for (IPluginService pluginService : loader.load()) {
+					for (PluginDescriptor<?, ?> descriptor : pluginService.load()) {
+						plugins.add(instantiate(descriptor));
+					}
+				}
+				return (DStreamCollection<? extends P>) (() -> plugins.stream().flatMap(ITypeRef.of(type)::castIfInstance));
+			}
+		};
+	}
+}

ha-plugin/src/test/java/com/g2forge/habitat/plugin/PluginService.java

@@ -0,0 +1,19 @@
+package com.g2forge.habitat.plugin;
+
+import com.g2forge.alexandria.adt.collection.CollectionCollection;
+import com.g2forge.alexandria.adt.collection.ICollection;
+import com.g2forge.alexandria.annotations.service.Service;
+import com.g2forge.alexandria.java.core.helpers.HCollection;
+import com.g2forge.alexandria.java.function.IFunction1;
+import com.g2forge.habitat.plugin.TestPluginSystem.Plugin;
+
+@Service(IPluginService.class)
+public class PluginService implements IPluginService {
+	@Override
+	public ICollection<PluginDescriptor<?, ?>> load() {
+		final PluginDescriptor.PluginDescriptorBuilder<Plugin, Plugin> retVal = PluginDescriptor.builder();
+		retVal.constructor(Plugin::create);
+		retVal.builder(IFunction1.identity());
+		return new CollectionCollection<>(HCollection.asList(retVal.build()));
+	}
+}

ha-plugin/src/test/java/com/g2forge/habitat/plugin/TestPluginSystem.java

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+package com.g2forge.habitat.plugin;
+
+import org.junit.Test;
+
+import com.g2forge.alexandria.java.core.helpers.HCollection;
+import com.g2forge.alexandria.test.HAssert;
+
+public class TestPluginSystem {
+	public static class Plugin {
+		protected static final Plugin INSTANCE = new Plugin();
+
+		public static Plugin create() {
+			return INSTANCE;
+		}
+
+		private Plugin() {}
+	}
+
+	@Test
+	public void test() {
+		HAssert.assertEquals(HCollection.asList(Plugin.create()), PluginSystem.getStandard().load(Plugin.class).load().toCollection());
+	}
+}